1. Field of the Invention
The present invention generally relates to semiconductor wafer processing and, in particular, to an apparatus for supporting semiconductor wafers during processing and for providing film uniformity improvements on wafers.
2. Description of the Related Art
Conventional wafer support mechanisms, such as susceptors, do not guarantee good film uniformity for single wafer tools. Often, these conventional susceptors yield films with poor and uneven uniformities, and with WOOPS (Wafer Out Of Pocket) errors, which results in subsequent reworking procedures. Moreover, conventional tools attempt to level the susceptor to prevent any sliding of the wafer. In fact, conventional tools use a leveling kit to set up the susceptor. However, the level of the susceptor shifts with time, thereby creating uniformity problems.
In the semiconductor wafer and substrate processing fields, various types of processing equipment are utilized which provide for automated handling of wafers in a vacuum environment. One of the more important concerns in the handling and processing of such wafer substrates is the need to minimize particle generation that could contaminate the wafers, subsequently damaging the devices being formed thereon. In an effort to ameliorate this, most semiconductor device fabrication is conducted within a “clean room” environment where extreme measures are taken to minimize the presence of particulate matter.
At a process station, it may be necessary to hold the wafer firmly against a support surface with a clamp during processing, for example, to maintain the position of the wafer relative to the processing equipment or to maintain good thermal contact to a heat transfer element. One conventional technique for maintaining the temperature of a wafer undergoing processing in a vacuum environment is to introduce a conductive gas in a narrow space at the backside of the wafer, thereby thermally coupling the wafer to a temperature control element. When using a backside gas, which is introduced at a pressure higher than the ambient pressure of the processing chamber, clamping means are required to ensure that the backside gas does not move the wafer off of the support surface.
In most cluster tool systems, and many other types of semiconductor processing systems, the wafers are loaded onto and removed from the process platform in a horizontal orientation. This allows gravity to be used to hold the wafer in place on the surface of the platform while the wafer is clamped and un-clamped. Therefore, unclamping normally involves simply translating the clamp mechanism in an upward direction, and relying on gravity to cause separation of the wafer and the clamp.
Unfortunately, the conventional methods used in a process chamber may cause the clamp to adhere to a wafer after completion of processing of the wafer at the process station, thus preventing the wafer from being picked up by the transport mechanism such as an automated clasp. For example, this may occur when a metal layer is deposited over a wafer which causes the wafer to stick to the clamp. Another example is when the top layer of a wafer melts at an elevated temperature, causing the top layer to adhere to the clamp.
When a semiconductor wafer sticks to a clamp, the processing system typically must be shut down to free the stuck wafer, a procedure that normally involves manual intervention at atmospheric pressure. After the process chamber is vented to atmosphere to permit manual wafer removal, it can take several hours before the chamber can be placed back in service due to the need to pump down the chamber and allow out-gassing of contaminants (e.g., water vapor, etc.) that have become adsorbed to the chamber surfaces. Thus, it can easily take several hours to recover from a stuck wafer.
Conventional systems have not adequately solved this problem. Moreover, the conventional systems have not adequately provided a device which improves the film uniformity of the semiconductor wafer undergoing processing. As such, wafers are constantly being processed with defects, thereby resulting in time consuming and costly rework procedures. Therefore, there is a need for a new and improved semiconductor wafer processing apparatus, which greatly improves the film uniformity of the wafer during processing, and which can be installed easily.